Modern gas turbines generally operate at extremely high temperatures. In addition, various components of a gas turbine, such as rotor support bearings, generate high temperatures due to friction forces and/or loads placed upon the gas turbine. As a result, high thermal stresses may significantly limit the mechanical life of the gas turbine. Therefore, it is necessary to provide a cooling medium to the gas turbine to prevent overheating and premature failure of the various components. Current methods for cooling and/or sealing the gas turbine include flowing a working fluid, such as compressed air and/or steam, to the various components of the gas turbine. Although current methods are generally effective, there is a growing concern over the long-term effects of Nitrous Oxides (hereinafter NOx), Carbon Dioxide (hereinafter “CO2”), Carbon Monoxide (hereinafter CO) and Sulfur Oxides (hereinafter SOx) emissions on the environment. The allowable levels of NOx and SOx that may be emitted by a gas turbine are heavily regulated. As a result, operators of gas turbines desire methods of effectively cooling the gas turbine while reducing the levels of NOx and SOx emitted.
Exhaust gas recirculation (EGR) generally involves recirculating a portion of the emitted exhaust through an inlet portion of the gas turbine where it is mixed with a working fluid, such as air, prior to combustion. This process facilitates the removal and sequestration of the emitted NOx, SOx, and concentrated CO2 levels, thereby reducing the net emission levels. However, impurities and/or moisture within the exhaust gas prevent utilizing a simple re-circulating loop to reduce the CO2, SOx, and NOx. As a result, turbine fouling, corrosion, and accelerated wear of internal gas turbine components would result from introducing the exhaust gas directly to the gas turbine for combustion and/or for use as a cooling medium. Therefore, the diverted exhaust gas should be treated prior to ingestion into the gas turbine. In addition, significant amounts of condensable vapors exist in the exhaust gas stream. These vapors usually contain a variety of constituents such as water vapor, acids, aldehydes, hydrocarbons, sulfur, and chlorine compounds. Left untreated, these constituents will accelerate corrosion and the fouling of the internal components, if allowed to enter the gas turbine through one or more cooling circuits of the gas turbine.
For the foregoing reasons, there is a need for a system that treats the recirculated exhaust gas stream to minimize the impact of harmful constituents within the exhaust gas stream and that flows the treated recirculated exhaust stream to at least a portion of the gas turbine for cooling and/or sealing.